1. Technical Field
The present invention relates to a ranging method in a mobile station of a femto system. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for a mobile station to perform a ranging on a femto base station in a mobile communication including a macro base station, the femto base station and the mobile station.
2. Background Art
Generally, IEEE 802.16m system includes legacy support functionality and is able to support IEEE 802.16e system. In case of a mixed mode, a base station (e.g., a macro base station, a femto base station, etc.) is operable using a frame including a WirelessMAN OFDMA region (hereinafter named an L region) supporting a legacy mobile station (i.e., IEEE 802.16e mobile station) and an improved wireless interface region (hereinafter named an M region) supporting IEEE 802.16m mobile station. Meanwhile, the base station is operable in a mode for supporting not a legacy mobile station but IEEE 802.16m mobile station only.
In a system supporting IEEE 802.16m mobile station only, a macro base station except a femto base station and a relay can use such a ranging channel structure for initial/handover ranging as shown in FIG. 1.
FIG. 1 is a diagram of a ranging channel structure available for a macro base station and a relay to perform initial ranging and handover ranging. Particularly, FIG. 1(a) shows Format 0 and FIG. 1(b) shows Format 1. In this case, the ranging channel can occupy contiguous frequency bands (i.e., a localized bandwidth) corresponding to 1 subband.
In FIG. 1, TRCP indicates a ranging cyclic prefix region and TRP indicates a ranging preamble region. As mentioned in the foregoing description, the ranging channel structure shown in FIG. 1 is usable for a ranging of a non-synchronized mobile station, i.e., for an initial ranging and a handover ranging.
Configuration information on Format 0 and Forma 1 is shown in Table 1.
TABLE 1Format No.TRCPTRPΔfRP0k1 × Tg + k2 × Tb2 × TbΔf/213.5 × Tg ÷ 7 × Tb8 × TbΔf/8
In Table 1, Δf indicates a subcarrier spacing, Tb indicates a useful symbol duration of OFDMA, i.e., Tb=1/Δf, Tg indicates a length of CP (cyclic prefix) of OFDMA, i.e., Tg=G·Tb, and G indicates a ratio of a useful symbol duration to a CP duration. Meanwhile, k1 and k2 meet the following conditions.K1=(Nsym+1)/2 and K2=(Nsym−4)/2  [Formula 1]
In Formula 1, Nsym indicates the number of OFDMA symbols within a single AAI subframe.
Based on the above described structure, in mode for supporting IEEE 802.16m only, ranging channel allocation information (i.e., configuration index and subframe offset (OSF)) is shown in Table 2, ranging code information (i.e., number Mns of cyclic shift codes per ZC root index) is shown in Table 3, and ranging preamble code partition information (i.e., NIN and NHO) is shown in Table 4.
TABLE 2ConfigurationsThe AAI subframe allocating Ranging channel0OSFth UL AAI subframe in every frame1OSFth UL AAI subframes in the first frame inevery superframe2OSFth UL AAI subframe in the first frame inevery even numbered superframe, i.e..mod(superframe number. 2) = 03OSFth UL AAI subframe of the first frame inevery 4−th superframe. i.e.mod(superframe number. 4) = 0
TABLE 3index0123Mns1248
TABLE 4Partition Index012345678901112131415Number of ini-8888161616162424242432323232tial ranging pre-amble codes. NINNumber of hand-8162432816243281624328162432over ranging pre-amble codes. NHO
A base station is able to transmit the informations shown in Tables 2 to 4 to a mobile station via S-SFH. As mentioned in the foregoing description, in a mode for supporting IEEE 802.16m only, since a base station transmit ranging channel information on initial ranging and handover ranging only via S-SFH, the ranging preamble code partition information, as shown in Table 4, includes the number (NIN) of codes of a code group for the initial ranging and the number (NHO) of codes of a code group for the handover ranging only.
Meanwhile, in a mode for supporting IEEE 802.16m only, a cyclic ranging channel can have the structure shown in FIG. 2 unlike the ranging channel for the initial ranging and the handover ranging shown in FIG. 1.
FIG. 2 is a diagram of a ranging channel structure for periodic ranging.
Referring to FIG. 2, in a periodic ranging channel, some of each OFDMA symbol region is copied as a cyclic prefix (hereinafter abbreviated CP) to a symbol head part. In FIG. 2, a length of a CP duration is represented as Tg and a useful symbol duration amounting to the rest region of an OFDMA symbol duration except the CP duration is represented as Tb. As mentioned in the foregoing description, Tb shown in FIG. 2 indicates Tb=1/Δf, Tg indicates Tg=G·Tb, and G indicates a ratio of a useful symbol duration to a CP duration.
Thus, the ranging channel information for the periodic ranging, the information necessary for code generation and information on a total number of codes available for a corresponding usage are delivered to mobile stations via AAI_SCD (advanced interface system configuration descriptor) message. Table 5 and Table 6 show information delivered via the AAI_SCD message.
TABLE 5Number of periodic rangingindexpreamble codes, NPE0 8116224332
TABLE 6ConfigurationsAAI subframe allocating ranging channel0mod(OSF ÷ 1 · NUL)th UL AAI subframein every frame1mod(OSF ÷ 1 · NUL)th UL AAI subframein the second frame in every superframe2mod(OSF ÷ 1 · NUL)th UL AAI subframein the second frame in every 4th superframe.i.e.. mod(superframe number. 4) = 03mod(OSF ÷ 1 · NUL)th UL AAI subframein the second frame in every 8th superframe.i.e.. mod(superframe number. 8) = 0
Table 5 shows code number information (NPE) of a code group available as partition information of a ranging preamble code for periodic ranging. And, Table 6 shows ranging channel allocation information on a periodic ranging channel.